Rotary impacting nut running tool



y 1957 w. s BRUCKER 2,792,732

ROTARY IMPACTING NUT RUNNING TOOL Filed Sept. 25, 1955 2 Sheets-Sheet l v IN VEN TOR.

WILLIAM S. BRUCK E R W k z k ATTORNEYS May 21, 1957 w. s. BRUCKER 2,792,732

ROTARY IMPACTING NUT RUNNING TOOL Filed Sept. 23, 1955 2 Sheets-Sheet 2 I N V EN TbR; BYWILLIAM s. BRUCKER Z K 1 k ATTORNEYS tROT-ARY IMPACTING NUT RUNNING TOOL WilliamSJBrucker, Towson, Md., assignor to The Black & Decker Manufacturing Company, Towson, Md a corporation of Maryland Application September 23, 1955,'Serial No. 536,125

6 Claims. (Cl. 81-525) This invention is concerned with impactingnut run- .ners of thecompression spring type wherein the connection between an accelerated hammer and the driving means comprises cams and balls.

In tools of this character, the practice has been to connect the hammer to a driving spindle through bearing balls which ride in V-shaped grooves formed on the ham- 'mer and driving spindle, whereby the relative motion taking place between the continually driven spindle and the hammer at theinstant of nut seating effects a cammed {separation of the impact lugs of the anvil and hammer by raising the hamer and its lugs out of clutched relationship with thetstalled anvil lugs. Usually such camming moves 'the' hammer axially against a compression spring, and as the hammer lugsrotate past the anvil lugs, the hammer isrestored .bythe spring to a position whereits lugs on continued.hammerrotation willagain engage the anvil ilugs in rotational impact, the camrning and impact cycle beingthen repeated. The practice has been to use helically shaped cams, i. e. cam formations with a constant lead, withthe result that at the instant of arrested rotary movement of the anvil lugs, therefore of the hammer, axial hammer motion theoretically must start at its full velocity .or rate per unit of relative spindle-hamrner angular displacement, or time rate velocity with assumed constant namically, when the hammer lugs haveimpacted on the r anvil lugs, some recoil of the hammer relativeto the anvil takes place, and an aggravated condition of shock occurs due to thehelical shape of the cams.

.By thepresent invention and discovery, the foregoing unfavorable operational action of the cams can be overcome by reducing the initial rate of acceleration of the axial movement of the hammer at the initiation of its separating movement relative to the anvil.

The general purpose of the present invention therefore is the provision of a tool of the type in question which will operate during protracted periods of use without the generation of excessive shock on the hammer driving spindle and cams of the tool.

Another object-of this invention is the provision in the impacting'mechanism of a pair of co-operating cam formationswhich will effect acceleration of the axial movement of the hammer in a gradual manner thereby substantially to eliminate shockto the driving elements upon initiation of upward movement of the hammer.

Another object is the provision of a'cam mechanism adapted to a more efficienttransfer of energy from. a driving motor to a spring element intended to accumulate energy to be released in rotational impact blows.

A further object of the present invention is the pro 'vision of cam formations and camming mechanisms for the above stated purposes which can "be'manufactured economically.

ted States Patent A still further object of the present invention is 'the provision of cam formations having camming surfaces which will be relativelyfiat with respectto the curvature of thebearingballstherebetween, thereby to avoid'the use of ball grooves which per se are friction producing because of extended ball contact.

Other objects and advantages will appear from the following description anddrawings, wherein:

"Fig. 1 is a side view of a motor driven impact wrench involving thepresent invention shown in partial axialsection;

Fig. 2 is an enlarged detail of the impacting mechanism in the axial section of Fig.1

Fig. 3 is an axial section taken substantially along the line 3--3 in Fig. 2;

Fig. 4 is a detail elevation of a cam element carrideby the spindle of the impact mechanism;

Fig. 5 is an elevational view taken at right angles to Fig. 4;

Fig. 6 is an end view of the camming surface corresponding to Fig. 4;

Fig. 7 is an axial section of a second cam element carried by thehammer of the impact mechanism;

Fig. 8 is an end view of the element of Fig. 7 showing the camming surface thereon; and

'Fig. 9 is a detailview showing the relation of the impact lugs.

InFig. 1, there is shown, as an electrically driven tool,

a portable impacting nut running wrench incorporating the present invention, including a motor casing 10 with attached handle 11; a trigger type motor switch 12 inthe handle; an electric motor within the casing 10',pre'ferably reversible, with armature or rotor 13 and motor shaft 14; a deep cup-likeimpact mechanism housing member 16 with'inner end counterbored to receive in close-slip fit a reduced shouldered end of the motor housing, and within housing 16, a mechanism couplingthe motor shaft to tool element 17, as hereinafter described in detail, adaptedto convert energy and continuous rotary motion available at the motor shaft under certain conditions into rotational impact upon a work piece, for example a nut or bolt engaged by a suitable tool element such as the :socket wrench element 17.

ferably a reversible electric motor with reversing switch means so that the tool may be used eitherfor tightening or loosening fasteners such as nuts or bolts. The housing elements 10 and 16 are secured together by such means as screws passed radially-through the coun'terbored end of 16 and threaded in the shoulder portion ofmember 10, or screws parallel to the axis securing radiallyprojecting adjacent corresponding integral lugs-on those members.

At the convergent left end of the housing member 16, a coaxial central here or aperture, aligned with the motor shaft axis, is fitted with a sleeve type bearing 18, flanged at its inner end for retention in the housing, to journal a shaft portion 19a of an anvil stud element 19 projecting through the housing to carry the work engaging tool element 17 on the outer end portion 1%, shown square in cross section to fit in a rotational driving relation the complementary recess of the tool element. The inner end of element 19 is enlarged to form integral angularly spaced anvil lugs 19c, symmetrical inindividual form and relative to the tool axis and in diametric relation to each other,having impact surfaces 19d parallel to the axis of the tool. The four impact surfaces 19d, roughly approximating but not in precisely radial disposition, for facility of manufacture are parallel to each other andare continued inwardlyto merge through a filet into the of motor housing to, there is a ring gear element 23 fixed against rotation by press fitting or other means, with which mesh a plurality of planet gears 24 rotatable on stud shafts 25 fixed in a planet carrier or cage 26. The cage is rotatably supported at one side by its central integral tubular extension 26a on the relatively rotatable motor shaft 14, the latter having a gear formation 14a cut on the end thereof as a sun gear meshing with planets 24; and at the other side by a spindle 29 with one end pinned at 39 in a second tubular extension 2612 and having the opposite reduced end 29a journalled in a coaxial bore 19 of anvil 19. The spindle 29 may however be an integral shaft extension of the planetary cage rather than secured thereto in the manner shown.

The shaft 14 has a shoulder outward of the end of cage extension 2611. Thus with rotor shaft bearings holding the shaft against any appreciable axial shift, the shaft shoulder bearing on the end of extension 26a and the shoulder at reduced spindle end 29a bearing on the anvil, the spindle, spindle cam 34 and planetary gearing assembly are held within housing 16 against any appreciable axial movement. The spindle 29 and cage extension 26a may be rotatably supported by the anvil and motor shaft and held against axial shift either directly as shown or through known bearing devices of apt form. The planetary system thus afiords a reduction gearing between the motor and the driving spindle 29 of the impact mechanism disposed coaxially with and between motor shaft 14 and tool element 17.

A hammer member 20, of generally hollow circular cylindrical shape, is supported for some degree of axial and rotational displacement relative to drive spindle 29 upon operation of the hammer lift camrning mechanism 32, '34, 37, 33 during impact action, by its end wall 20a coaxially apertured for rotational and sliding bearing on the spindle; and through the cam mechanism hereinafter described, by a symmetrical hollow hammer lift cam member 32 (Figs. 7, 8) of circular cylindrical external form inserted into, and secured against relative axial and rotational displacement in, the open or right end of the hollow hammer and having a bore 32a through which with clearance extends the left end of cage tubular exten sion 26b, or the spindle where spindle and cage are integral. Arch-like cam surfaces of member 32 face toward the anvil end of the mechanism. The hammer lift cam member is held with a small circumferential spacing in the hammer by diametrically opposite aligned fasteners 33 serving as trunnions allowing to cam member 32 a limited degree of pivotal movement about the fastener centerline. The fasteners 33 may be dog point set screws threaded through diametrically opposed threaded radial apertures of the cylindrical hammer wall with the dowellike points of the screws extending as trunnions into and bearing on bottom surfaces of corresponding reamed holes 32b in the cam element 32. Snap rings within the threaded apertures may be used to hold the screws 33, and so also to hold pins or screws at 30 and 35. On the closed left end of the hammer element 26, there is a pair of hammer lugs 2G0, individually symmetrical in form and in diametric relation, extending endwise from the hammer element toward the anvil with impact faces 20b parallel to the tool axis disposed complementary to the impact areas of faces 19d for engagement and impact with matching impact areas of corresponding faces on the anvil lugs.

A symmetrical spindle lift cam member 34 (Figs. 4-6), having a portion 34a with circular cylindric external surface extending into the counterbore 32c and end face portions 341; having clearance relative to counterbore shoulder 32d in the opposed end of cam 32 when the hammer is moved to the extreme left position of Fig. 2, is secured to the drive spindle 29 by a radial pin 35, the cam surfaces thereof facing away from the anvil end in opposed relation to the cam surfaces on 32. A pair of hardened cam balls 36 are interposed between the two cam elements, each ball lying between corresponding op posed cam surfaces 32e and Me of hammer and spindle cam members respectively.

The limited pivotal motion of the hammer cam element 32 about fasteners 33 accommodates larger manufacturing tolerances than would otherwise be possible, particularly in the cams, without adversely affecting the functioning of the tool.

The central aperture of spindle cam 34, through which the spindle 29 extends, is counterbored at 34c to a depth beyond surface Me to accommodate the left end of the cage tubular extension 26b. A heavy prestressed helical compression spring 37, biasing the hammer toward the anvil, is located within the hollow hammer to bear endwise directly on the hammer end wall 20b, and mediately on. the spindle cam through a bearing cup member 38 having a radial rim flange 38a to engage the corresponding end of the spring, a cylindrical wall portion 38b surrounding with clearance a portion of the length of a reduced end 34d on the spindle cam as a bearing centering means and a plurality of bearing balls 39 located in the annular space between spindle 29, the left end of cam 34, and the centrally apertured end wall 38c and cylindrical wall 38b of cup 38 to form a thrust bearing between the spindle and spring in its ultimate function.

In the hammer lift cam 32 of the drawing, the arch shaped camming surfaces 32s are symmetrically diametrically formed relative to the cam element axis, therefore to the tool axis-the common axis of the coaxially aligned shaft 14, spindle 29, anvil l9, hammer 20 and spindle cam 34-as portions of a single theoretical circular cylindric surface intersecting the hollow cylinder of the hammer cam with axis spaced beyond the working end of the cam and also perpendicular to the cam axis. Such cam surfaces may be formed on a hollow cylindrical hammer cam blank end at one pass by milling diametrically thereacross with a rotary cutter having suitably shaped cutting edges.

In the spindle lift cam 34 also, the camrning surfaces 34a are symmetrically formed and diametrically disposed relative to the cam element axis, and hence so located relative to the tool axis. The major portions of these cam surfaces are portions of corresponding theoretical planes equally oblique to the axis and angularly disposed as faces of a dihedral angle, the dihedral edge of which intersects at right angles the axis of this cam element. The axis lies in the bisecting plane of the dihedral angle. However, in approaching the dihedral edge the cam surfaces become curved surfaces 34e diverging from the dihedral faces as appears in Fig. 5, with the terminal portions of the actual cam surfaces approaching parallelism with the cam element axis and forming definite partitions between the two camming surfaces of opposed slope. The Working end of the spindle cam is therefore roughly wedge-shaped. The particular constants of the cam surface shapes are chosen to attain curved paths of ball contact therewith such that rolling contact of the balls is ensured.

Thus the spring 37 biases the hammer and therefore the hammer lift cam 32 to the left, toward the anvil, so that the anvil lugs 192 would lie in the path of rotation of the hammer lugs 20a. The ball elements in the camming mechanism are captive between the inner round cylindrical surface of the hammer, the cam surfaces 322, the cam surfaces 34:: sloping in a direction in major part away from surfaces 32a in a radially outward direction with the relative positions of Figs. 2 and 3, and tubular extension 26b, though the wedging action of surfaces 32a in spreading the balls apart into contact with the inner surface of the hammer keeps each ball out of contact with the extension for only three point contact with the other noted surfaces under all normal operating conditions. Also with the balls so spread into contact with the hammer, the upper end of the hammer is piloted (Jr-supported relative to the spindle through-the balls and rest of the cammingmechanism.

With the hammer free'for rotation relative to the spindle, the cam elements assume the position of Figs. land 3 under the force of spring 37. Upon rotation of the spindle in either direction by themotor, the hammer lugs contact the anvil lugs as appears for clockwise rotation in Fig. 2 or Pig. 9 to rotate the anvil and tool element 17, the force of the spring being sufiicient to maintain the relations of the engaged cam elements as in Figs. 2 and 3 as long as thetool element is not rotationally impeded, for example during the free running of a nut on or ofi a bolt or stud.

When element 17 is impeded, say upon seating of a nut after free running, or when the tool is applied to remove a seated nut, the hammer is then held against rotation. As the spindle cam is driven further by the motor, effecting a relative angular displacement or advance of cam element34re1ative to element 32 from the neutral position of Figs. 2 and 3, the balls are displaced from their positions lowest or innermost relative to the ends of the respective cam surfaces up the cam slopes with ball angular displacement relative to each cam corresponding to substantially equal paths of rolling contact (or to half the relative angular cam displacement for simplified analysis in a non-quantitative sense), displacing the hammer axially away from the anvil thereby compressing spring 37, until the hammer lugs escape the anvil lug impact faces. As such compression is effected, energy is stored in the compressed spring. Thereupon the hammer is free to rotate in the. direction of spindle rotation; and, when thetend faces of the lugs have cleared each other, for the compressed spring to move the hammer axially to bring the hammer lugs into the space between the anvil lugs for again achieving impact engagement of the lugs at the impact faces. However, as the hammer moves axially forward toward the anvil under spring force, thereby returning the elements of the cam mechanism toward neutral position, a relative motion of the hammer to the spindle in the direction of spindle rotation is attained, converting the potential energy stored by the spring compression during the preceding lagging hammer displacement into kinetic energy of the hammer accelerated thereby.

This kinetic energy, additive to the energy supplied by the motor through the rotating spindle upon hammer escape, results in a strong rotational impact force of hammer upon anvil to tighten or loosen a seated nut. The free angular space, represented by the difference between 180 and the sum of the angular extent of a hammer and anvil lug provides time for the acceleration by the motor of the gearing, spindle cam and hammer total mass as Well as acceleration of the hammer with respect tothe spindle before a consequent impact. Where recoil of the hammer takes place after an impact, the recoil effects a relative motion between spindle and hammer in the same sense as a corresponding initial static engagement of hammer and impeded anvil with attendant lift of the hammer by the cam system, spring compression and accumulation of potential energy in the spring. The potential energy of the spring is of course available for conversion into kinetic energy as previously described, additive to the kinetic energy acquired by the rotating impactor system acceleration before another impact.

The continued rotation of the spindle by the motor causes a repetition of such impact cycle and a rapid success-ion of rotational blows as usual in tools of this character to effect a desired degree of tightening within the capabilities of the tool. The strength of the spring, its degree of precompression and the power and operating characteristics of the motor are chosen by the ordinary design considerations for the tool capacity required.

Considering the geometrical relations of the camming mechanism in the operation just described, it will first tightening or loosening operation.

-be n'oted'-thatthecontact path of 'a-ball on a surface-34,

i. e. the planecam surface portion, is a .portion of a plane curve, approximatelyan ellipse oblique to the tool axis and-having a' m ajor axis passing through the tool axis. Thus-at the neutral position of Figs. 2 and 3, such ballhas a point of contact with surface 34e at the end of the major axis the lowermost point of the path, and lying on-aline there tangent to the ellipse and accordingly to the circledescribed about the tool axis during rotation by such lowermost point, i. e., the end point of the majoraxis. Thereforeat the'beginningof relativeangular displacement in either direction between the cams, the pressure angle of cam 34 on the ball is zero, incontrast with "the considerable angle of a helical cam forsuch service. "Of 'course,inthe case of cam 32, the contactpathof the ballon surface 322 is not a plane curve, but rather a skew curve, approximately lying in a circularcylindric surface'coaxial-to the tool and broadly being a portionof the intersection, with the latter surface, of a theoretical second cylindric surface (ofwhich 32e is a portion) generatedbya generatrix line (defining, at its continuously'success'ive positions, the cylindric-elements of the surface) moving perpendicular to a plane includingboththe corresponding directrix curve and the axis of the tool rotation, the directrix being symmetrical to the axis of rotation. However, the ball has at neutral position 'a point of contactwith 32 lying on a tangent to the low point of the'path'and accordingly tothe circle describedby thatllow point about the tool axis during rotation, sothathere toothe pressure angle of balland cam 32 is zero'as just noted for cam 34. In the specific form of 'the drawing, the theoretical cylindric surface corresponding to 32c 'iscircularly cylindric. ,The net elfect .then at the instant'of beginning relative angular displacementin either directionlbetween the cams, since 'the pressure angles are zero, isthat there is not a theoretically necessary axial motion of some finite value instantaneously imparted to the hammer with infinite acceleration; and in a, practical sense shock due to such cause is in fact substantially obviated, a result ofparticular value during the series of repeated impacts involved in a nut In--a practical sense the above analysis and operative results obtain, even though some slight tilt of the hammer lift cam out of coaxial relation with the tool axis occurs for accommodation of manufacturing tolerances.

By inspection it may be seen that from the initial neutral position aboveanalyzed, as relative angular displacement occurs between spindle cam and hammer cam to lift the hammer, the slopes of the ball contact paths thereon increase, so the axial hammerdisplacement occurs at an increasing rate in terms of relative angular displacement; thoughas to time rate, as themotor speed drops off with increasing spring reaction, in the latter part of angular displacement, the time rate actually drops off. Hammer axial acceleration in terms of time increases from a relatively low initial value to a maximum,

drops to zero and becomes negative as the axial hammer velocity decreases to zero under spring resistance. In terms of the relative angular displacement, the axial motion component imparted by cam 34 is harmonic in quality; and by hammer cam 32, a modification of a cyclic motion.

I claim:

1. In a tool of the character described, a hammer driving spindle, a rotary anvil and a hollow hammer, cooperating impacting lugs on the anvil and on the hammer, said hammer being displaceable in a rotational and axial sense relative to said driving spindle, energy accumulating means comprising a compression spring reacting on the spindle and hammer normally to maintain the hammer and anvil lugs in engagement during nut running operation of the tool, andmeansfor axiallyshiftingthe hammer away from the anvil upon arrested "movement of the anvil in opposition to the influence of the spring;

the second said means comprising a hammer cam member fixed on the hammer having a pair of arch-shaped cams facing toward the direction of the anvil and disposed 180 apart, a wedge-shaped cam member having a pair of plane cams formed at an obtuse dihedral angle to each other and symmetrically converging toward the axis of the spindle and disposed on the spindle 180 apart, said plane cams facing in a direction away from the anvil and normally in opposed relation to the archshaped cams on the hammer, and a bearing ball interposed between each set of opposed cams; said hollow hammer having an internal circular cylindrical surface serving to retain the balls in rolling relation to the said cams.

2. In a tool of the character described, a hammer driving spindle, a rotary anvil, a hollow hammer having one end open and an opposite end wall, cooperating impacting lugs on the anvil and on the hammer end wall, said hammer being mounted coaxially about the driving spindle and being displaceable in a rotational and axial sense relative thereto, energy accumulating means comprising a compression spring within the hollow hammer reacting on the spindle and hammer end wall normally to maintain the hammer and anvil lugs in engagement during nut running operation of the tool, and means located within the hollow hammer for axially shifting the hammer away from the anvil upon arrested movement of the anvil in opposition to the influence of the spring; the second said means comprising a hammer cam member fixed in the open end of the hammer and having a pair of arch-shaped cams facing inward of the hammer and disposed 180 apart, the spindle extending through a bore in said cam member and the cam member being counterbored between the cams, a pair of flat spindle cams shaped to be obliquely symmetrically converging toward the axis of the spindle and disposed on the spindle 180 apart, said flat spindle cams being extended in the counterbore of the hammer cam member normally in opposed relation to the arch-shaped cams on the hammer, and bearing ball means interposed between each set of opposed cams, said hollow hammer having an internal circular cylindrical surface portion serving to retain said ball means in rolling relation between the opposed cams.

3. In a tool of the character described, a hammer driving spindle, a rotary anvil and a hollow hammer, cooperating impacting lugs on the anvil and on the hammer, said hammer being displaceable in a rotational and axial sense relative to said driving spindle, energy accumulating means comprising a compression spring reacting on the spindle and hammer normally to maintain the hammer and anvil lugs in engagement during nut running operation of the tool, and means for axially shifting the hammer away from ie anvil upon arrested movement of the anvil in opposition to the influence of the spring; the last said means comprising a hollow cylindric hammer I cam member fixed on the hammer with the spindle extending coaxially therethrough, said cam member having a cylindric trough-like formation across an end thereof with the cylindric elements perpendicular to a plane including the spindle axis whereby are formed a pair of arch-shaped cams facing toward the direction of the anvil and disposed 180 apart, a spindle cam member of circular cylindric external shape with one end projecting into the end of the trough formed end of the hollow hammer cam member, said one end of the spindle cam member being substantially cuneate to form a pair of plane cams at an obtuse dihedral angle to each other disposed on the spindle 180 apart and symmetrically converging toward the axis of the spindle, said plane cams and arch-shaped cams being normally in opposed relation, and a bearing ball interposed between each set of opposed cams and having a single point of contact with each cam, said hollow hammer having an internal circular cylindrical surface serving to retain the balls in rolling relation to the said cams.

4. In a tool of the character described, a hammer driving spindle, a rotary anvil and a hollow hammer, cooperating impacting lugs on the anvil and on the hammer, said hammer being displaceable in a rotational and axial sense relative to said driving spindle, energy accumulating means comprising a compression spring reacting on the spindle and hammer normally to maintain the hammer and anvil lugs in engagement during nut running operation of the tool, and means for axially shifting the hammer away from the anvil upon arrested movement of the anvil in opposition to the influence of the spring; the second said means comprising a hollow cylindric hammer cam member fixed on the hammer with the spindle extending coaxially therethrough, said cam member having across an end thereof a symmetrical circularly cylindric trough-like formation with the cylindric elements perpendicular to a plane including the spindle axis whereby are formed a pair of arch-shaped cams facing toward the direction of the anvil and disposed apart, a spindle cam member of circular cylindric external shape with one end projecting into the end of the trough formed end of the hollow hammer cam member, said one end of the spindle cam member being substantially cuneate to form a pair of plane cams at an obtuse dihedral angle to each other disposed on the spindle 180 apart and symmetrically converging toward the axis of the spindle, said plane cams and arch-shaped cams being normally in opposed relation, and a bearing ball interposed between each set of opposed cams and having a single point of contact with each corresponding cam, said hollow hammer having an internal circular cylindrical surface serving to retain the balls in rolling relation to the said cams.

5. In a tool of the character'described, a hammer driving spindle, a rotary anvil, a hollow hammer having one end open and an opposite end wall, cooperating impacting lugs on the anvil and on the hammer end wall, said hammer being mounted coaxially about the driving spindle and being displaceable in a rotational and axial sense relative thereto, energy accumulating means comprising a compression spring within the hollow hammer reacting on the spindle and hammer end wall normally to maintain the hammer and anvil lugs in engagement during nut running operation of the tool, and means located within the hollow hammer for axially shifting the hammer away from the anvil upon arrested movement of the anvil in opposition to the influence of the spring; the second said means comprising a hammer cam member fixed in the open end of the hammer and having a pair of con cave end cams facing inward of the hammer and disposed 180 apart in rotational symmetry relative to the spindle axis, the spindle extending through a bore in said cam member and the cam member being counterbored between the cams, said end cams being portions of a common cylindric surface having cylindric elements perpendicular to a plane including the spindle axis and each having the axially innermost portion thereof tangent to a plane perpendicular to the spindle axis, a pair of flat spindle cams shaped as portions of planes obliquely symmetrically converging toward the axis of the spindle, the spindle cams being disposed on the spindle 180 apart in rotational symmetry relative to the spindle axis, said flat spindle cams being extended in the counterbore of the hammer cam member normally in opposed relation to the cams on the hammer, and bearing ball means interposed between each set of opposed cams, said hollow hammer having an internal circular cylindrical surface portion serving to retain said ball means in rolling relation between the opposed cams.

6. In a tool of the character described, a hammer driving spindle, a rotary anvil and a hollow hammer, cooperatin impacting lugs on the anvil and on the hammer, said hammer being displaceable in a rotational and axial sense relative to said driving spindle, energy accumulating means comprising a compression spring reacting on the spindle and hammer normally to maintain the hammer and anvil lugs in engagement during nut running operation of the tool, and means for axially shifting the hammer away from the anvil upon arrested movement of the anvil in opposition to the influence of the spring; the second said means comprising a hollow cylindric hammer cam member with the spindle extending coaxially therethrough, aligned pivot means diametrically disposed to the spindle axis securing the hamer cam member to the hammer against relative axial and rotational displacement While permitting a limited self-adjusting pivotal motion therebetween, said cam member having across an end thereof a symmetrical circularly cylindric trough-like formation with the cylindric elements perpendicular to a plane including the spindle axis whereby are formed a pair of arch-shaped cams facing toward the direction of 15 2539678 the anvil and disposed 180 apart, a spindle cam member of circular cylindric external shape with one end projecting into the end of the trough formed end of the hollow V hammer cam member, said one end of the spindle cam member being substantially cuneate to form a pair of 20 plane cams at an obtuse diheral angle to each other disposed on the spindle 180 apart and symmetrically converging toward the axis of the spindle, said plane cams and arch-shaped cams being normally in opposed relation, and a bearing ball interposed between each set of opposed cams and having a single point of contact with each corresponding cam, said hollow hammer having an internal circular cylindrical surface serving to retain the balls in rolling relation to the said cams.

References Cited in the file of this patent UNITED STATES PATENTS 2,160,150 Jimerson et al May 30, 1939 Thomas Jan. 30, 1951 2,716,475 Mitchell Aug. 30, 1955 FOREIGN PATENTS 466,339 Great Britain May 26, 1937 

